Metal finishing or metal plating plants, as well as electronic plants which make printed circuit boards, use water in the plating process which, when becoming waste water, is known as "plater's rinse water". This plater's rinse water contains remnants of copper or tin. Various processes to remove copper or tin from plater's rinse water have been proposed. Electrolysis is one of these processes; others are evaporation, and chemical precipitation.
The referenced U.S. Pat. No. 4,399,020, the disclosure of which is hereby incorporated by reference, describes an arrangement to remove metals from plater's rinse water, with or without recycling. An electrically conductive solution is placed in a trough or cell box of insulating material in which a plurality of alternatively located plate-like anodes or cathodes of spongy construction are inserted. The cathodes are pervious to the liquid and the waste water passes through the cathodes essentially perpendicular to their plate surface. Cations of the metals in the waste water are deposited on the cathodes.
It has been found that, as the cell is used for a long period of time, the pores of the cathodes will close due to the metal deposition thereon, resulting in a continuous reduction of the actual cathodic surface, and, as a consequence, a rise in specific cathodic current density. The final metal concentration is then limited by economics. The initially spongy cathodes become plugged, and throughput of the cell is decreased. Consequently, the cathodes must be frequently renewed.